US2295048A - Refining of mineral oils - Google Patents

Description

Sept. 8, 1942. R. F.. P'FENNIG REFINING' OF MINERAL QILS Q. NJN

Filed Patented Sept. 1942 REFNHNG OF MINERAL OILS Reuben F. Pfennig, Goose Creek, Tex., assigner to Standard Oil Development Company, a corporation of Delaware Application October 5, 1940, Serial No. 359,820

13 Claims.

This invention relates Vto the refining of mineral oils and is particularly concerned with an improved process for the refining of petroleum oils. In accordance with the invention, petroleum oils are treated in an initial stage with an anhydrous molten alkali and then treated in a secondary stage with a solvent-having the ability to separate the alkali reaction .products from the feed oil. A tertiary treating stage may be employed for further rening of the oil such as solvent extraction, acid or clay treating or solvent dewaxing. The preferred modifications of the present invention comprise contacting feed petroleum oils boiling in `thelubricating oil boiling range with an anhydrous molten alkali at a temperature above the fusion point of the alkali, separating the treated oil from the anhydrous alkali treating agent and removing the reaction products therefrom by treating the same with a liquefied normally gaseous hydrocarbon.

It is well known in the art to refine and process mineral oils and petroleum hydrocarbons by various procedures in order to produce refined products of the desired quality. In these operations it is desired to produce finished products of high quality which are characterized by being neutral or non-acid, by being relatively stable in that deterioration of 'the product Will not occur over a relatively long period of time,

and by having asatisfactory color and color stability. Thus various processes are directed specically to the productionof neutral, stable, and -color satisfactory products -in the rening of mineral oils such as in the processing of low boiling petroleum oils, motor fuels, kerosenes, cracked naphtha fractions, heating oil fractions, lubricating oils, wax fractions, as well as solvent extracts.

For example, in the processing of lubricating oil stocks derived from naphthenic crudes, `it is known that certain constituents such as naphthenic acids and the like must be removed for the production of neutral distillates. A conventional procedure for accomplishing this result is to inject aqueous solutions of sodium hydroxide or equivalent solutions directly into the still, preheater, or fractionating tower and to allor the distillation to .proceed in the presence of this alkali. Various modifications of this process are also employed, one of which is to inject dry lime into the preheater or still in order to neutralize acidic compounds, particularly naturally occurring acidic oxygen-containing compounds, which results in an improvement in the color and Vquality of the refined oil. It is also Vknown topass mixtures of petroleum vapors and steam through strong aqueous alkali solutions .at elevated temperatures. Another practice is v'to contact petroleum vapors with fused caustic in a distillation tower by circulatingthe liquid caustic over several plates near the bottom of the tower. By operating in this manner, the vapors from the still are passed countercurrently through the liquid caustic, 'thus neutralizing acidic materials and effecting a color stability improvement in the distillate. Hydrocarbon oils have also been extracted with aqueous solutions of Vsodium 'hydroxide at relatively high temperatures, for example, in the range from about 300 F. 'to A400" F.

and at elevated pressures such as 300 pounds to Z pounds per square inch. However, While accomplishing satisfactoryresultsin general, these processes possess certain disadvantages which increase operating dilculties and renderthe operations relatively expensive. A distillation operation conducted .in Vthe .presence of a solution of sodium hydroxide tends to cause .deposition of the caustic on the walls of the equipment and heating means, which materially .decreases heat transfer rates and increases operatingcosts. Furthermore, 'it 4is necessary to frequently 'clean the equipment, thus substantially decreasing `its yearly throughput. Other disadvantages encountered in current processes are "the extensive pressure drops which are incurred, particularly in vacuum distillation operations, as well as inthe formation of emulsions which are difficult to break.

I have now discovered a ,process for the production of high' yields of improved quality products which have abetter resistance to oxidation and coke formation thanhas heretofore been secured by known processes. My process comprises contacting a mineral oil, ,particularly a petroleum oil, boiling in the lubricating oil boiling range in an initial stage with a fused anhydrous valkali at a `temperature above the -fusion .point of the alkali and then contacting the oil after .removal of the alkali in a secondary stage with a solvent having the ability to remove the-alkali reaction products. The preferredmodication of my invention comprises contacting the feed oil in an initial stage with an alkali mixture and then treating the contacted oil Yin a secondary stage with a liqueed normally ,gaseous hydrocarbon solvent. My process produces `finished rproducts which have a low neutralization value and which have exceptionally good cast Vas well as high stability against oxidation and coke or carbon formation without the necessity of a distillation operation. In accordance with my process the feed oil is contacted in the liquid phase at relatively low pressures and at temperatures below the point at which cracking of the feed oil occurs.

The process of my invention may be readily understood by reference to the attached drawing illustrating one modification of the same. The feed oil, which for the purposes of illustration is assumed to be a petroleum oil boiling in the lubricating oil boiling range, is withdrawn from storage tank I and passed through heat exchanger 2 by means of line 3 and pump 4. The oil is then passed through a heating unit or furnace 5 and introduced into treating unit 6 by means of line 1. In treating unit B the oil is contacted at the desired temperature and pressure with a fused alkali solution which is withdrawn from storage 8 and introduced into treating unit 6 by means of pump 9 and line I0. The alkali treated oil is withdrawn from treating unit 6 by means of line II, passed through heat exchanger 2 and then introduced into cooler I2. 'Ihe cooled mixture is withdrawn from cooler I2 by means of line I3 and treated with a solvent having the ability to remove the alkali reaction products.

For purposes of illustration it is assumed that the solvent comprises liquefied propane which is introduced into the system by means of line I4. The alkali treated oil and propane are introduced into settler I5 by means of line I6. The desired temperature conditions are maintained in settler I5 by means of steam heating unit I1 or an equivalent means. The treated oil product free of the alkali, the alkali reaction products and other undesirable constituents is withdrawn from settler I5 by means of line I8 and further refined or handled in any manner desirable. One finishing procedure is to pass the oil from the settler I5 through line I 8 to solvent extractor equipment 20 wherein the oil is contacted with a selective solvent of the class having perferential selectivity for the relatively more aromatic constituents as compared to the relatively less aromatic constituents such as phenol supplied through line 2|, thereby forming a solvent extract phase and a raffinate phase, separating the two phases and recovering the thus purified oil from the raffinate through line 22 by removing the solvent from that phase in still 23 The treated oil may be dewaxed, acid and clay treated lor otherwise refined in order to produce the desired refined product. The alkali reaction products, together with asphaltic and other undesirable constituents present, are withdrawn from settler I5 by means of line I9 and likewise handled or disposed of in any manner desirable.

The process of the present invention may be widely varied. The operation essentially comprises a two stage process in which a mineral oil, particularly a petroleum oil (distillate or residuum), boiling in the lubricating oil boiling range is treated in an initial stage with a fused alkali at a temperature above the fusion point of the alkali and then contacted in a secondary stage with a solvent having the ability to remove the alkali reaction and other undesirable products. Although the process may be adapted to the treatment of many feed oils, it is particularly applicable to the treatment of relatively high boiling asphalt-free petroleum oil fractions such 'as high quality lubricating oil products and various specialty oil products. In general, the feed oil preferably comprises petroleum oils having gravities in the range below about 30 to 35 A. P. I.

Although any hydrous fused alkali may under certain conditions be employed, we prefer to utilize anhydrous alkali metal hydroxides, such as sodium hydroxide and potassium hydroxide. An especially desirable treating agent comprises a mixture of sodium hydroxide and potassium hydroxide, particularly when the concentration of the sodium hydroxide is in the range from about 25% to 85%. In general, the most satisfactory operation is secured when the sodium hydroxide, potassium hydroxide mixture comprises from 45% to 55% of sodium hydroxide. Other desirable alkali mixtures comprise sodium hydroxide admixed with various anhydrous inorganic salts which are capable of lowering the fusion point of the sodium hydroxide. Particularly desirable salts-are sodium carbonate, sodium sulde, sodium bromide, sodium iodide and sodium sulfate. An especially desirable alkali mixture utilizing sodium hydroxide comprises a mixture of sodium hydroxide and anhydrous sodium carbonate. When employing this mixture, it is desirable to use at least '75% sodium hydroxide, preferably from to 95% sodium hydroxide. A particularly suitable mixture comprises 92% sodium hydroxide and 8% sodium carbonate. The alkali should be substantially anhydrous and in no instance should the moisture content of the alkali or alkali mixture exceed about 2.0%. In general, the moisture content of the alkali treating agent should be below about 0.5% and should preferably be anhydrous.

Th-e time of contact between the fused anhydrous alkali or alkali mixture and the oil is a function of the intimacy of contact obtained between the oil and alkali. The time of contact will also depend upon the character of the feed oil, the quantity of alkali utilized and the particular alkali or alkali mixture employed. In general, it is preferred to contact the oil for a period from about 5 to 25 minutes, preferably from 10 to 20 minutes, at a suitable temperature ranging between about 370 F. to 700 F. A particularly desirable operation is to contact the oil at a relatively high temperature which is bclow the temperature at which cracking of the oil occurs.

The quantity of anhydrous fused lalkali used per volume of feed material will vary considerably and will depend upon lthe above-mentioned factors. In general, the quantity of fused alkali employed will vary in the range from about 0.1 to 3.0 volumes of alkali per volume of feed material. Usually, it is preferred to employ from 1.0 to 1.5 volumes of anhydrous fused alkali per volume of feed material. The fused alkali preferably is settled and removed from the treated oil before the latter is contacted with the solvent, although in certain operations this may not be necessary.

The solvent employed may be any solvent having the ability to remove the alkali reaction products from the treated oil. In general, solvents having the ability to deasphalt the oil are suitable. Solvents of this class are for example hexane and light virgin naphtha fractions, employed under suitable conditions of elevated temperature and pressure. However, in general the preferred solvents are liqueed normally gaseous hydrocarbons, particularly propane or mixtures comprising propane. The quantity of solvent em. ployed per volume of oil will depend upon tne lparticular oil being treated and the character of the alkali `reaction and `other undesirable -prod- 4uc'ts present, and will lalso depend to a larger-ex- "tent upon the nature of the solvent or solvent mixture employed. For example, when employing :propanelas the solvent, it is preferred to use fromabou't 3 to 7 volumes of propane per Volume pfeil. The temperature-employed in the secondfary stage will similarly depend upon theV partieular ifeedoilbeing treated as well as upon the solvent being u-sed. For example when employing propane, -the preferred temperature is in the rangelfroma-bout 110 F. -to 140 F.

`In order to further illustrate my invention, `the following examples are given which should not be construedas limiting the same in any manner whatsoever.

Example 1 A parafnic `residual oil from a Panhandle `In operation (A) a portion of this oil was in- .timately -mixed at 550 F. with an excess of a molten alkali,vcomprising about 92% sodium hydroxide and aboutS% sodium carbonate.

.'Ihe treated oil was separated from the alkali treating agent and contacted at about 129 F. with 500% by volume of liquid propane. The treated oil was separated from the precipitated alkali reaction products and handled in a manner to vremove the .propane and then dewaxed using labout Vfour'volumes of naphtha per Volume of oil at 30 F. 'The oil after removal of the waxy constituents and naphtha was acid treated with 35 pounds of sulphuric acid per barrel of oil at 65 F. in a solution c-f four volumes of propane per volume of oil. After removal of the. acid and propane, the oil was clay contacted at 400 F. with 0.35 pound of clay per gallon of oil.

In operation (B) another portion of the residual oil was handled in a manner described with respect to operation (A) except that the alkali treating step was-omitted.

A portion of the treated oils secured from operations (A) and (B) Were solvent extracted utilizing -phenol as the selective solvent.

The inspections on the respective oil products are as (follows:

TABLE I I nspectzons of the treated products Not Solvent Solvent Tgagd treated free free fused with raffinate raffinate alkali fused of oil of 011 alkali (l) (2) Oil product (l) (2) (3) (4) Color, Tag Robinson 3% 3% 3 2% Gravity, A. P. I.- 26. 2 26.0 27.4 27.0 Viscosity index 99 100 106 105 Ramsbottom coke A 0.76 0.78 0.60 0. 68 Ramsbottoln coke BA 1. 38 1. 58 0. 99 1.05 Conradson carbon residue percent 1.07 1. 26 0.86 1.05 Bomb sulphur do 0.50 0. 54 37 .47 Neut. value mg. KOH/gm.. 0. 01 0. 01 01 01 Pour F 25 25 30 30 From the above data, it is readily apparent that the carbon residue or coke-forming characteristics of oil products treated in accordance with the present process is greatly improved and that the solvent extracted alkali and propane treated oil is-'especially desirable.

-It will be noted that two values of Ramsbottom .coke test are reported; namely, Ramsbottom coke A .and lRamsbottom coke B--A. The A value is obtained by subjecting Yan un- -oxidized sample of the oil to the normal Ramsbottom coke test described in the A. S. T. -M. Tentative Standards and designated as Vmethod D 524-39'1. According to C. .-I. `Kelley `(Carbon residue estimation on .lubricating oils, Petroleum Times, April 8, 1938, pages 429-31) this test bears a linear relation to the well-.known Conradson carbon residue test. The B Value is obtained by subjecting to the Ramsbottom coke test A a sample of oil which has previously been-oxidized for 12 hours at .200 C. `in accordance with the method described in the British 'Air Ministry General Specification for Mineral Lubricating Oil, Specification D T. D. 109 as of January 1936. Obviously the B-A Value vis obtained by subtracting the A value from the B value `and is used `to indicate the coke-forming tendency of an oil under service conditions.

Example 2 A portion of a resi'duum o-btained from a Coastal crude was alkali treated as described in Example l and a Vaporous product removed overhead by distillation. The un'distilled fraction boiling in the lubricating oil range was submitted to treatment for the removal of the `alkali reaction products using vlidueiied propane in the manner described at :a temperature of about The product .freeof `propane and the alkali reaction product'was dewaxed, acid treated at 75 F. and clay contacted as described in Example 1. In another operation a similar portion of a residuum obtainedfrom the Coastal crude was likewise treated in the identical manner except that the alkali treatment was omitted. Inspections Vonv the .products secured'by .the respective operations are as follows:

Table II Inspections of the treated product From the above data, it is readily apparent that the quality of the treated product is materially improved by employing the process of the present invention.

The present invention is not to be limited by any theory or mode of operation but only in and by the following claims in which it is desired to claim all novelty in so far as the prior art permits.

I claim:

1. Process for'the production of rened mineral oil of improved quality which comprises treating a mineral oil with an anhydrous fused alkali at a temperature above the fusion point of thealkali but below the temperature at which cracking of the oil occurs, then contacting the treated oil with a low boiling liquefied hydrocarbon material under conditions to separate the alkali reaction products from the treated oil.

2. Process for the production of mineral oils of improved quality comprising 'treating a mineral oil with an anhydrous fused alkali at a temperature above the fusion point of the alkali but below the temperature at which cracking of the oil occurs, whereby alkali reaction products are formed, then contacting the treated oil with a liquefied normally gaseous hydrocarbon under conditions to separate the alkali reaction products from the thus treated oil.

3. Process in accordance with claim 2 in which said liquefied normally gaseous hydrocarbon comprises propane.

4. Process for the production of refined petroleum oils having a relatively low carbon content Which comprises treating a petroleum oil in an initial stage with an anhydrous fused alkali at a temperature above the fusion point of the alkali but below the temperature at which the cracking of the oil occurs, whereby alkali reaction products are formed, removing the treated oil from the fused alkali and treating the same in a secondary stage with a liquefied normally gaseous hydrocarbon under conditions to separate the alkali reaction products from the treated oil.

5. Process in accordance with claim 4 in which said alkali comprises sodium hydroxide and in which said liqueed normally gaseous hydrocarbon comprises propane.

6. Process in accordance with' claim 4 in which said alkali comprises a mixture of 85% to 95% sodium hydroxide and from -5% sodium carbonate and in which said liqueed normally gaseous hydrocarbon comprises propane.

'7. Process for the production of oils boiling in the lubricating oil boiling range and having a relatively low carbon content*l from asphalt-free feed'oils which comprises contacting an asphaltfree petroleum oil boiling in the lubricating oil boiling range with an anhydrous fused alkali at a temperature above the fusion point of the alkali but below the temperature at which cracking of the oil occurs, whereby alkali reaction products are formed, removing the spent anhydrous alkali from the treated oil, and contacting said oil with a liquefied normally gaseous hydrocarbon under conditions to separate the alkali reaction products.

8. Process for the production of high quality petroleum oil products which comprises contacting a petroleum oil in an initial stage with an anhydrous fused alkali at a temperature above the fusion point of the alkali but below the temperature at which cracking of the oil occurs whereby alkali reaction products are formed, removing the treated oil from the alkali and subjecting the treated oil in a secondary stage to treatment with a liquefied normally gaseous hydrocarbon under conditions to separate the alkali reaction products, segregating the treated oil and contacting the same in a tertiary stage with a selective solvent of the class having a preferential selectivity for th'e relatively more aromatic constituents as compared to the relatively less aromatic constituents under conditions to form a solvent extract phase and a raffinate phase, separating the phases and removing the solvent therefrom.

9. Process in accordance with claim 8 in which said fused alkali comprises a mixture of sodium hydroxide and sodium carbonate.

10. Process for the production of rened products of improved quality from the residuum fractions of crude petroleum comprising heating the residuum to a temperature in the range from about 370 F. to '700 F., intimately contacting the heated residuum with a substantially anhydrous fused alkali reagent at a temperature above the fusion point of the alkali but below the temperature at which the cracking of the oil occurs, settling and separating the treated residuum from the excess alkali reagent, returning the excess alkali reagent to the treating step, cooling the alkali treated residuum and diluting th'e same with a low boiling liquefied hydrocarbon material whereby the alkali reaction products are precipitated, settling and separating the diluted oil from the precipitated materials, and recovering the solvent from the treated oil by distillation.

il. Process in accordance with claim 10 in which the low boiling liquefied hydrocarbon material is a liqueed normally gaseous hydrocarbon,

l2. Process in accordance with claim 10 in which the fused alkali reagent is a substantially anhydrous mixture comprising sodium hydroxide in amounts from about 20 to 100% and potassium hydroxide in amounts in remaining proportions.

13. Process in accordance with claim 10 in which the fused alkali reagent is a substantially anhydrous mixture comprising sodium hydroxide in amounts from about to 100% and sodium carbonate in amounts in remaining proportions. v

REUBEN F. PFENNIG.

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